For several years, studies that relate human aggression (including hyperactivity and conduct disorder in children) and suicide to various behavioral and biological factors have been ongoing. Some of the most significant findings have included pharmacokinetic and metabolic studies of amphetamine administered to hyperactive and conduct disordered children, and a trivariate relationship among a history of aggressive behavior, a history of suicidal behavior, and lower cerebrospinal fluid (CSF) 5- hydroxyindoleacetic acid (5HIAA). More recently, data indicate that certain aggressive, impulsive, and depressive characteristics in childhood are also inversely related to CSF 5HIAA measured during late adolescence; family instability during childhood also appears to be associated with increased likelihood of aggressive and/or suicidal behavior in late adolescence. These data, along with the work of other investigators studying aggressive behavior in childhood, indicate the possibility of traits associated with disordered serotonin metabolism; further, the less consistent relationship between lower CSF 5HIAA and suicidal behaviors vs. aggressive behaviors, may indicate that some suicidal behaviors are a self-destructive manifestation of a more basic destructive (aggressive/impulsive) trait.